Circular Dichroism (CD) spectrometry is a very important tool in sensing chiral molecular structures which don't superimpose onto their mirror image. Chiral structures are very recurrent in biological media and organic compounds. Therefore, CD spectrometers find many applications in areas including, but not limited to, biological sensing, stereochemistry, crystallography and DNA structural analysis.
CD spectrometers measure the spectrum of differential absorption between left circularly polarized (LCP) light and right circularly polarized light (RCP). Conventional prior art CD spectrometers measure LCP and RCP spectra sequentially. The laser sources are tuned to generate LCP across the wavelength range and measure the absorption, and then, the source is switched to RCP and the process is repeated. The process is time consuming, and involves much complicated hardware to switch the polarization of the laser, thereby increasing the dimensions of the device.
Polarization gratings have been proposed to split LCP and RCP spatially. The gratings can be used to obtain real-time concurrent measurement of LCP and RCP spectra. This can eliminate the need to use complicated switchable sources. However, these polarization gratings require large thickness to accumulate optical phase delays between the major and minor axes of polarization gratings. Therefore, improvements are needed in the field.